The present invention generally relates to a method for generating a formula for calculating mottling of a paint film, and a quantification method of the mottling.
It is practiced that colors are blended such that a color desired by a user is obtained. At that time, success or failure of blending is determined by evaluating performance such as paint finish performance, paint film performance, and paint material performance of an actually blended paint. However, user preference is highly diversified, and the number of colors required by users can be as great as the number of the users. For this reason, past data are often inapplicable, and testing of each color is required, resulting in the need for a large amount of manpower and time.
Under situations as described above, it is highly desired that a calculation formula (prediction formula) be established such that performance of a blended paint is predicted, and only a successful blending is provided to the users.
In order to determine successful blending without performance problems, information about performance, such as the paint finish performance, the paint film performance, and the paint material performance, is quantified and evaluated based on past actual results, etc. Here, the paint finish performance is related to skin, gloss, mottling, sagging, pinholes, workability to a production line, etc; the paint film performance is related to durability (degree of degradation due to the sunlight), corrosion resistance (degree of degradation due to rust and water), adhesion, chipping nature, hardness, electric resistance, gloss, chemical resistance, etc.; and the paint material performance is related to storage durability, dilution stability, circulation-proof nature, etc.
In this manner, the performance of a blended paint is predictable, and whether an acceptable quality of the paint is obtainable can be determined using the information described above, and the problem about time and effort is solved.
However, in the case that a paint contains glittering color material (such as metal flakes, and pearlescent mica), the color of the paint changes with viewing angle, and evaluation of the mottling is especially difficult.
In this connection, JP, 5-288690, A (patent reference 1) discloses “A paint mottling determination method of a metallic paint film”, wherein by an irradiation process, a laser light having a beam diameter of 5-to-10 mm is irradiated to the surface of a target (to be measured) paint film of a metallic paint, and the laser light is irradiated at a predetermined angle of incidence, and by a light-receiving process, the laser light reflected by the target paint film is received. The irradiation process and the light-receiving process are carried out at two or more contiguous spots that are apart from each other by a distance equal to or less than the laser beam diameter, and optical brightness of the reflected light that is received is calculated at two or more predetermined wavelengths, which process is repeated for all the spots. According to the optical brightness at the predetermined wavelengths of all the spots, the degree of paint mottling is determined.
Further, JP, 9-318448, A (patent reference 2) discloses “A mottling determination apparatus and an evaluation method of metallic paints” wherein a light is irradiated to a target paint surface, the brightness of the reflected light is continually measured, the reflected light being received at angles at which mirror reflection light is not received (i.e., the specularly reflected light being excepted), and a degree of mottling of the surface of the target paint is determined by calculating (1) the difference between the brightness of the received light that exceeds an average of the measured brightness by a predetermined amount, and the brightness that is less than the average of the measured brightness by the predetermined amount, and (2) the distance between a spot that gives the brightness that exceeds the average by the predetermined amount, and a spot that gives the brightness that is less than the average by the predetermined amount.
Nevertheless, according to the inventions disclosed by the patent references 1 and 2 presented above, the amount of reflected light is measured only along a predetermined line on the paint film, and only the brightness is considered in determining the mottling. For this reason, precision of the mottling determination is not sufficient. In other words, the mottling, which essentially is a two-dimensional object, is determined based only on measurement data along a line (one dimension), and only the brightness, and the mottling of the surface in two dimensions cannot be properly determined.